DVB provides a standard for the distribution of digital broadcast video content. One of the issues concerning the adoption of DVB is that the pristine digital content provided by the standard could potentially be recorded and distributed without loss of quality and without the content owner's consent. To avoid unauthorized distribution the DVB standard includes a mechanism for encrypting the distributed content prior to transmission. DVB, however, does not dictate a digital rights management (DRM) scheme or key delivery standard. These two elements ensure the secure transmission and conditional access to the protected content. DVB leaves this aspect of content protection to the development of proprietary DRM systems.
In any rights managements system encryption of the delivered content is relatively simple. What is more difficult is distributing conditional access to the rights needed to decrypt and use the distributed information. Rights embody what an end user is allowed to do with the encrypted content, for example, play the content for a certain period or copy the content a limited number of times. DRM accomplishes this conditional access to the content by wrapping the keys required to decrypt the content into a tightly controlled system where the rights themselves cannot be freely copied or distributed, see Published U.S. Patent Application No. 2003-0076955-A1. The successful control of these rights requires that they be individualized to restrict distribution of the rights beyond a particular authorized end user.
Current DVB DRM solutions transmit these rights as vouchers sent along with the same broadcast that carries the DVB transmission. This approach can be very wasteful of bandwidth because each user needs to receive an individualized rights voucher. As the number of vouchers grows the broadcast link's bandwidth, which must also carry the digital content, will be needlessly wasted. This method of voucher transmission is particularly wasteful because every user that receives the broadcast receives not only the voucher intended for that user but also the vouchers intended for every other user.
Other approaches to provide DRM control utilizing specialized equipment, such as set top boxes with smart cards and modems, to distribute rights vouchers through different communications links, for example over telephone lines. However, the specialized equipment required to carry out the rights delivery prevents over-the-air broadcasters from efficiently controlling an end user's equipment the way a cable distributor might. The problem is that while the over-the-air broadcasters would like to develop additional broadcast pay systems, they cannot without first developing a unified hardware infrastructure for the end users, including DRM infrastructure (hardware and software) and billing mechanisms. The investment required to create a system would be substantial for any one broadcast channel. Additionally end users would be unlikely to invest in or acquire new equipment for a system that worked for one only channel.